When filling a cartridge chamber of a cartridge with a filling mass, it is common practice to close the cartridge chamber by inserting a piston into the cartridge chamber containing the filling mass. That means a piston is set or inserted into the cartridge chamber. It is desirable not to trap air in the cartridge chamber during this setting operation due to the fact that air may be harmful for the component stored in the cartridge chamber and due to the fact that air as a compressible gas may cause the piston to tilt when moved for discharging the filling mass from the cartridge. Additionally, the presence of a compressible gas will cause a pressure variation inside the chamber during dispensing which creates undesirable variations in flow and may result in poor performance of discharged material.
According to DE 298 00 594 U, a micropore filter is inserted into a pocket formed in the piston. By means of this micropore filter, the air trapped between the filling mass and the piston can escape when the piston is inserted into the cartridge. Furthermore, this micropore filter is to prevent any emission of the filling mass. However, volatile components of the filling mass can penetrate the micropore filter, which may lead to leakage.
DE 295 06 800 U shows another ventilation device. Here, the ventilation is performed by means of a plurality of valve plugs mounted around a divided circle of the piston cover, and these plugs are lifted from valve cones when the piston is pressed into the cartridge, thus enabling the discharge of air. However, this ventilation device can only be manufactured with tight manufacturing tolerances. Another disadvantage can be seen in that parts of the filling mass can advance up to the valves, which are then contaminated, so that their sealing function is adversely affected.
A cartridge piston is also known from DE 200 10 417 U1. The piston has a first piston part which is provided with a sealing lip which is designed for contact with the cartridge wall. The first piston part has a circular cylindrical recess. Furthermore, the piston has a second piston part which has a circular cylindrical wall part which is latched to the first piston part at the base of the recess and thus forms a latch connection. The circular cylindrical wall part merges in arcuate form into a valve pin of a venting valve. This valve pin passes through a cylindrical bore arranged along the piston axis in the first piston part and has a valve cone which comes into contact with a valve lip of the first piston part. The latch connection is interrupted by a small air passage which forms a filter path between the circular cylindrical wall part and the first piston part. The filter path is made up of narrow passages at the inner wall of the circular cylindrical wall part.
If the cartridge piston is inserted into a cartridge, the valve pin is moved such that the venting valve is opened and the air enclosed between the filling mass and the cartridge piston escapes via the air passage and the filter path and is discharged via the venting valve. If the cartridge piston is pressed toward the filling mass, filling mass can move via the air passage up to the filter path, but is prevented by the labyrinth formed by the filter path from being discharged through the venting valve.
Additionally, many materials packaged in cartridges are very viscous and form irregular surfaces rendering current piston setting techniques ineffective. Such irregular surfaces are in general not flat, but may comprise a plurality of peaks and valleys of irregular shape.
It is the object of the invention to provide a cartridge piston with a piston setting device which allows for a faster setting of the piston, thus for higher discharge rate of air.
The system and the piston setting device according to the invention allows the extraction of unwanted air between the fluid mass and piston by creating a negative pressure differential between fluid mass and cartridge piston.
At the same time, the valve remains dry and free of dirt. Creeping, oil-like components of the filling masses should be prevented from leaking from the valve.